The present invention relates to a control system for a clothes dryer for household use.
In the prior art clothes dryer of a type wherein wet clothes are dried by the application of hot air while tumbled inside the rotating drum, it is usual to employ a mechanical timer for presetting an operating duration during which the dryer is operated according to the quantity or type of the clothes. The presetting of the mechanical timer requires the operator to have a knack or skill in the determination of the operating duration and, therefore, a difficulty has been encountered in the determination of an operating duration appropriate to a given quantity or type of clothes. It has also been often experienced that, if the operating duration is not properly set in the mechanical timer, the clothes are either excessively or insufficiently dried and/or some of the clothes are impaired. As a matter of course, the excessive drying brings about an additional problem in that unnecessarily increased amount of electric power is consumed.
A system wherein the surface resistance of the clothes being dried detected by the use of elecrodes to determine the extent to which they are dried is also well known in the art. This system is, however, disadvantageous in that, since the surface resistance varies with the type of clothes, an accurate detection of the dryness of the clothes is difficult to achieve. In view of this, this system has been improved to include an exhaust temperature sensor for detecting the temperature of exhaust air vented from the inside of the rotating drum and is so designed that, while the detection of the surface resistance is carried out by the use of the electrodes until the clothes are dried to a certain extent, the exhaust temperature sensor can be utilized to subsequently determined the time at which the drying operation is to be brought to a halt, in dependence on the rate of increase of the temperature of the exhaust air. Even this improved system has a problem in that, since two separate elements such as the exhaust temperature sensor and the electrodes are required, the structure tends to become complicated. Moreover, since a relatively high voltage is required to detect a high surface resistance by means of the electrodes, this often poses an additional problem associated with the safety factor.